BackgroundInfections acquired in hospital are an important cause of morbidity and mortality in very preterm infants. Several small trials have suggested that supplementing the enteral diet of very preterm infants with lactoferrin, an antimicrobial protein processed from cow’s milk, prevents infections and associated complications.ObjectiveTo determine whether or not enteral supplementation with bovine lactoferrin (The Tatua Cooperative Dairy Company Ltd, Morrinsville, New Zealand) reduces the risk of late-onset infection (acquired > 72 hours after birth) and other morbidity and mortality in very preterm infants.DesignRandomised, placebo-controlled, parallel-group trial. Randomisation was via a web-based portal and used an algorithm that minimised for recruitment site, weeks of gestation, sex and single versus multiple births.SettingUK neonatal units between May 2014 and September 2017.ParticipantsInfants born at < 32 weeks’ gestation and aged < 72 hours at trial enrolment.InterventionsEligible infants were allocated individually (1 : 1 ratio) to receive enteral bovine lactoferrin (150 mg/kg/day; maximum 300 mg/day) or sucrose (British Sugar, Peterborough, UK) placebo (same dose) once daily from trial entry until a postmenstrual age of 34 weeks. Parents, caregivers and outcome assessors were unaware of group assignment.OutcomesPrimary outcome – microbiologically confirmed or clinically suspected late-onset infection. Secondary outcomes – microbiologically confirmed infection; all-cause mortality; severe necrotising enterocolitis (NEC); retinopathy of prematurity (ROP); bronchopulmonary dysplasia (BPD); a composite of infection, NEC, ROP, BPD and mortality; days of receipt of antimicrobials until 34 weeks’ postmenstrual age; length of stay in hospital; and length of stay in intensive care, high-dependency and special-care settings.ResultsOf 2203 enrolled infants, primary outcome data were available for 2182 infants (99%). In the intervention group, 316 out of 1093 (28.9%) infants acquired a late-onset infection versus 334 out of 1089 (30.7%) infants in the control group [adjusted risk ratio (RR) 0.95, 95% confidence interval (CI) 0.86 to 1.04]. There were no significant differences in any secondary outcomes: microbiologically confirmed infection (RR 1.05, 99% CI 0.87 to 1.26), mortality (RR 1.05, 99% CI 0.66 to 1.68), NEC (RR 1.13, 99% CI 0.68 to 1.89), ROP (RR 0.89, 99% CI 0.62 to 1.28), BPD (RR 1.01, 99% CI 0.90 to 1.13), or a composite of infection, NEC, ROP, BPD and mortality (RR 1.01, 99% CI 0.94 to 1.08). There were no differences in the number of days of receipt of antimicrobials, length of stay in hospital, or length of stay in intensive care, high-dependency or special-care settings. There were 16 reports of serious adverse events for infants in the lactoferrin group and 10 for infants in the sucrose group.ConclusionsEnteral supplementation with bovine lactoferrin does not reduce the incidence of infection, mortality or other morbidity in very preterm infants.Future workIncrease the precision of the estimates of effect on rarer secondary outcomes by combining the data in a meta-analysis with data from other trials. A mechanistic study is being conducted in a subgroup of trial participants to explore whether or not lactoferrin supplementation affects the intestinal microbiome and metabolite profile of very preterm infants.Trial registrationCurrent Controlled Trials ISRCTN88261002.FundingThis project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full inHealth Technology Assessment; Vol. 22, No. 74. See the NIHR Journals Library website for further project information. This trial was also sponsored by the University of Oxford, Oxford, UK. The funder provided advice and support and monitored study progress but did not have a role in study design or data collection, analysis and interpretation.